A grant has been awarded to Dr. Daniel Nickrent at Southern Illinois University Carbondale that will fund molecular phylogenetic and biogeographical (= phylogeographical) research on a group of parasitic plants called mistletoes. Although related to the Christmas mistletoes (family Viscaceae), this family (Loranthaceae) differs in several ways including flower morphology, pollination mechanisms, and geographic distributions. Whereas Viscaceae are thought to have originated on the northern Laurasian landmass, Loranthaceae evolved on the southern supercontinent called Gondwanaland. The origins of a number of plant families can be traced to Gondwanaland, and one (Nothofagaceae - the southern beeches), has been considered a model for examining the biogeographical history of the southern landmasses. Surprisingly, despite knowledge of its morphology, fossil history and phylogeny, the evolutionary origin of Nothofagus remains controversial. The research proposed here will use Loranthaceae as another model group that can be used to investigate similar biogeographical questions. Loranthaceae provide several advantages over other plants in that they have limited ability for long-distance dispersal (a factor that can complicate such biogeographic analyses) owing to their parasitic habit and host requirements . Endemic and relictual loranth genera occur on all the continents that were formerly part of Gondwanaland, thus offering many opportunities to conduct modern phylogeographical analyses.
The proposed study has four primary objectives: 1) to use nuclear and chloroplast gene sequences to generate a molecular phylogeny of Loranthaceae; 2) to use the above molecular phylogenetic results to test existing biogeographical hypotheses for the family based upon chromosome number; 3) to use the resulting phylogeny to examine evolutionary patterns in morphological features such as the inflorescence, and 4) to provide a revised classification of the family. This work will attempt to be comprehensive in scope, thus sampling all or nearly all of the existing 73 genera in the family. These objectives will be achieved by building phylogenetic trees from DNA sequence data. These trees will then be transformed into taxon distribution (area) cladograms that can then be analyzed using a variety of procedures based upon cladistic principles.
This work is significant because Loranthaceae represent the largest family in the sandalwood order, a family for which no modern classification or phylogeny exists. These mistletoes are a major component of tropical and subtropical ecosystems in the southern hemisphere and have been the focus of research from diverse fields such as pollination biology, cytology, coevolution with birds, and biogeography. For these reasons, a phylogeny of the family will prove extremely valuable to others wishing to place their data in the proper evolutionary context. For example, interpretation of inflorescence morphology has traditionally proven extremely difficult in many plant groups. Loranthaceae show a wide range of inflorescence types and a well-resolved molecular phylogeny will allow one to determine, for example, whether simple inflorescences arose via reduction from more complex ones or whether evolution proceeded with the opposite polarity. This research will be a component of the education and training of graduate and undergraduate students in field, laboratory, and analytical methodologies. Many of the loranth genera are susceptible to extinction owing to human-caused habitat destruction or other unknown factors. Thus the proposed collection of loranth DNA represents a unique and valuable resource not only for phylogeographic studies but also from the perspective of gene-banking. This project helps meet the challenges of the biodiversity crisis, as summarized by the Systematics Agenda 2000, by generating a predictive classification system on Loranthaceae, a parasitic plant group that can serve as indicators of ecosystem integrity and function.
